1. Field of the Invention
The present invention relates to a hub and, more particularly, to a ratchet hub for a bicycle.
2. Description of the Related Art
A conventional hub for a bicycle in accordance with the prior art shown in FIGS. 10 and 11 comprises a shaft 70, a hub body 60 rotatably mounted on the shaft 70, a ratchet wheel 61 secured in the hub body 60 to drive the hub body 60 to rotate relative to the shaft 70 and having an inside provided with a plurality of oneway ratchet teeth 611, a drive seat 50 rotatably mounted on the shaft 70 and having a first end provided with a support base 52 which is rotatable in the ratchet wheel 61 and has a periphery provided with a plurality of receiving slots 521, a plurality of pawl members 53 each pivotally mounted in a respective one of the receiving slots 521 of the support base 52 and each meshing with the oneway ratchet teeth 611 of the ratchet wheel 61 so that the ratchet wheel 61 is combined with and rotatable with the support base 52 of the drive seat 50, a plurality of elastic members 54 each biased between the support base 52 of the drive seat 50 and a respective one of the pawl members 53, two first bearings 72 and two bushings 73 mounted between the drive seat 50 and the shaft 70, and two second bearings 720 mounted between the hub body 60 and the shaft 70. The drive seat 50 has a second end provided with a sprocket 51.
In assembly, the hub body 60 is connected to a wheel (not shown) of the bicycle, and the shaft 70 is connected to a frame (not shown) of the bicycle. The sprocket 51 of the drive seat 50 meshes with and is driven by a chain (not shown) which is driven by a chainwheel (not shown) which is driven by a pedal (not shown) that is pedalled by a rider.
In operation, when the pedal is pedalled by the rider to move forward, the chainwheel is driven by the pedal to drive the chain which drives the sprocket 51 of the drive seat 50 to rotate the drive seat 50 forward relative to the shaft 70, so that each of the pawl members 53 is rotatable forward with the support base 52 of the drive seat 50. At this time, each of the pawl members 53 meshes with the oneway ratchet teeth 611 of the ratchet wheel 61 so that the ratchet wheel 61 is driven by the pawl members 53 to drive the hub body 60 to rotate relative to the shaft 70 to move the wheel forward. On the contrary, when the pedal is pedalled by the rider to move backward, the chainwheel is driven by the pedal to drive the chain which drives the sprocket 51 of the drive seat 50 to rotate the drive seat 50 backward relative to the shaft 70, so that each of the pawl members 53 is rotatable backward with the support base 52 of the drive seat 50. At this time, each of the pawl members 53 passes by the oneway ratchet teeth 611 of the ratchet wheel 61 so that the ratchet wheel 61 is released from the oneway ratchet teeth 611 of the ratchet wheel 61. Thus, the ratchet wheel 61 together with the hub body 60 is not driven by the drive seat 50, and the drive seat 50 idles in the backward direction.
However, when each of the pawl members 53 passes by the oneway ratchet teeth 611 of the ratchet wheel 61 during the backward rotation of the drive seat 50, each of the pawl members 53 touches the oneway ratchet teeth 611 of the ratchet wheel 61 to produce noise due to the friction, thereby easily causing an uncomfortable sensation to the rider. In addition, when the hub body 60 is rotated in the backward direction (e.g., when the wheel is rotated backward), the ratchet wheel 61 is also rotated in the backward direction. At this time, each of the pawl members 53 meshes with the oneway ratchet teeth 611 of the ratchet wheel 61 so that the ratchet wheel 61 drives each of the pawl members 53 to drive the drive seat 50 to rotate relative to the shaft 70 in the backward direction. Thus, the pedal is driven by the drive seat 50 to rotate backward so that the rider is easily hit and hurt by the pedal, thereby causing danger to the rider.